Three-dimensional articles can be replicated from a master that can be used to fabricate a tool for microreplication. A number of technologies have been developed to make tools or molds for microreplication or nanoreplication of three-dimensional articles. These technologies include conventional photolithography and two-photon photolithography. Additionally, three-dimensional articles can be fabricated using a nonlinear thermal polymerization process.
Some microstructures such as, for example, microneedles or microneedle arrays have features that have a high aspect ratio—that is, they have a large length or height compared to their diameter. The ability to write structures using two photon-photolithography with high aspect ratios in three dimensions requires very thick layers of photoresist—particularly if the structures need to be fabricated vertically. During the development state, where unexposed photoresist is removed to reveal the desired three-dimensional structure, the developer fluid, typically a solvent for the unexposed photoresist, can be absorbed or swelled by the exposed photoresist—particularly when the development step takes long periods of time such as hours. The formed three-dimensional structure is then dried to remove the solvent. The swelling and then shrinking due to solvent removal ultimately leads to structures with reduced fidelity to the structure that was written by the two-photon exposure.